Patent Document 1 (Japan Patent Application, Publication No. S55-4956) shows a swash plate pump. The pump housing has a cone formed in its spherical space, and an oblique disk is fitted in the spherical space with its center on the top of the cone. The oblique disk can rotate about the center axis of the cone while being kept both in contact with the conical surface and the inner spherical surface of the housing. The cone has one radius groove made on its conical surface, and a partition plate is movably fitted in the groove so that it may swing while constantly abutting on and following the oblique disk, thereby defining variable capacity compartments between the cone and the oblique disk. The cone has supplying and discharging through holes made right next to the partition plate. This type of pump is simple in structure and is relatively small in size. It works quietly, discharging fluid almost continuously. Also, reversal operations are permitted to drive fluid in the opposite directions.
It is, however, necessary that such swash plate pump be equipped with check valves for pressure feeding, and accordingly the pump size is increased. Also disadvantageously, an operation of the valves causes noise and significant quantities of power loss. Furthermore, the inner spherical surface of the enclosure wall is rubbed all the time by the oblique disk to be worn, causing leaks in the pump to lower its durability.
With a view to reducing such defects, inventors of the present invention have proposed an improved swash plate pump described in Patent Document 2 (Japan Patent Application, Laid-Open No. 2001-3876). It comprises: a cone rotatable about its center axis, a disk confronting the cone with their center axes crossing, a spherical enclosure wall integrated with the cone, and a partition plate movably fitted in one diametrical groove made in the cone. The partition plate moves in the groove while constantly abutting on and following the disk, thereby dividing a cone-and-disk confronting space into separate variable capacity compartments. In operation, the cone and the disk are rotated in synchronization about their center axes.
With this arrangement, a stationary abutment line is defined at the radius of the disk at which the disk is kept contact with a conical surface while rotating. Different from the case with the conventional swash plate pump, the speed of the disk relative to the surrounding spherical wall is reduced, thereby improving the durability of the pump and also expanding applicable types of fluid to dry kind, which does not cause any lubrication at rubbing surface. Supplying and discharging through holes are made in the disk that rotates, and these through holes can be timely opened and closed to form a gating structure, thereby getting rid of check valves. The so improved swash plate pump can supply and discharge fluid quietly at an increased efficiency. Disadvantageously, the swash plate pump of Patent Document 2 allows a discharging pressure in the selected variable compartments to be applied to the rotary members along their axes, thereby separating the disk from the cone to allow fluid to leak across the abutment line. This inhibits an increase of the discharging pressure beyond a certain limit. Also disadvantageously, application of the discharging pressure to the disk at even low level makes it rub the spherical wall with an increased force, causing lowering of the durability of the pump due to thermal expansion and significant wear.
In the hope of solving these problems, bearings are designed to provide controlled counter pressure or spring means are used to cause the same effect, but these will induce significant power loss. The axial rigidity of the rotary members and the housing supporting them cannot be enforced without increasing the weight and size of the pump. In order to increase the flow rate and the discharging pressure, and to widen applicable type of fluid to include vacuum pumping, it is necessary that: no leak be caused at the rubbing areas; gas be compressed under the lubrication-free rubbing condition; and a correct timing be assured in supplying and discharging operations in response to the fluid-pressure.
Fluid-pressure exploiting machines of similar structure which are responsive to application of pressurized fluid for rotation such as in a hydraulic motor have these problems in common. As a matter of course, the problems other than leakage across the abutment line need to be solved in all the swash plate type variable capacity fluid machines, including swash-plate vane type fluid machines having variable capacity compartments formed by a plurality of vanes.